Various additives have been used to improve the overall performance of rubbery products. For example, tires are often subjected to rough road conditions that produce repetitive, localized high-pressure pounding on the tire. These stresses can cause fatigue fracture and lead to crack formation and crack growth. This degradation of the tire has also been referred to as chipping or chunking of the tread surface or base material. In an attempt to prevent this degradation, it is known to add reinforcements such as carbon black, silicas, silica/silanes, or short fibers into the tire formulation. Silica has been found advantageous due to its ability to deflect and suppress cut prolongation, while silanes have been added to bind the silica to unsaturated elastomers. The fibers that have been added include nylon and aramid fibers.
It is also known that the addition of polyolefins to rubber compositions can provide several beneficial properties. For example, low molecular weight high density polyethylene, and high molecular weight, low density polyethylene, are known to improve the tear strength of polybutadiene or natural rubber vulcanizates. In the tire art, it has also been found that polyethylene increases the green tear strength of carcass compounds and permits easy extrusion in calendaring without scorch. Polypropylene likewise increases the green strength of butyl rubber. Polypropylene has also been effective in raising the static and dynamic modulus of rubber, as well as its tear strength. However, the addition of polyolefin to tire recipes may also have a deleterious effect on other mechanical and wear properties of tires, as well as handling and ride of the tire.
Over the past several years, polymer nano-particles have attracted increased attention not only in the technical fields such as catalysis, combinatorial chemistry, protein supports, magnets, and photonics, but also in the manufacture of rubber products such as tires. For example, nano-particles can modify rubbers by uniformly dispersing throughout a host rubber composition as discrete particles. The physical properties of rubber such as moldability and tenacity can often be improved through such modifications. Moreover, some nano-particles such as polymer nano-strings may serve as a reinforcement material for rubber in order to overcome the above-mentioned drawbacks associated with polyolefin and silica reinforcement. For example, polymer nano-strings are capable of dispersing evenly throughout a rubber composition, while maintaining a degree of entanglement between the individual nano-strings, leading to improved reinforcement. Selection of nano-particles having suitable architecture, size, shape, material composition, and surface chemistry, etc., would best improve the rubber matrix characteristics. In addition, nano-particles of good thermostabilities are more desirable for rubber articles.
Advantageously, the present invention provides a method for preparation of nanoparticles having a vulcanizable shell and a core of high glass transition temperature (Tg). The nanoparticles may be used as, for example, additives for rubber products such as tires.